109 lines
6.7 KiB
HTML
109 lines
6.7 KiB
HTML
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<meta name="DC.Title" content="Environment variables" />
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<meta name="abstract" content="You can use environment variables to override default initialization of resolver functions." />
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<link rel="stylesheet" type="text/css" href="./ic.css" />
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<title>Environment variables</title>
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</head>
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<body id="cenviron"><a name="cenviron"><!-- --></a>
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<!-- Java sync-link --><script language="Javascript" src="../rzahg/synch.js" type="text/javascript"></script>
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<h1 class="topictitle1">Environment variables</h1>
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<div><p>You can use environment variables to override default initialization
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of resolver functions.</p>
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<div class="section"><p>Environment variables are only checked after a successful call
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to <span class="apiname">res_init()</span> or<span class="apiname"> res_ninit()</span>. So if
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the structure has been manually initialized, environment variables are ignored.
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Also note that the structure is only initialized once so later changes to
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the environment variables are ignored. </p>
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</div>
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<div class="section"><div class="note"><span class="notetitle">Note:</span> The name of the environment variable must be capitalized. The
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string value might be mixed case. Japanese systems using CCSID 290 should
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use uppercase characters and numbers only in both environment variables names
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and values. The list contains the descriptions of environment variables that
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can be used with the <span class="apiname">res_init()</span> and <span class="apiname"> res_ninit()</span> APIs.</div>
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</div>
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<div class="section"><h4 class="sectiontitle">LOCALDOMAIN</h4><p> Set this environment variable to a
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space-separated list of up to six search domains with a total of 256 characters
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(including spaces). This overrides the configured search list (struct state.defdname
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and struct state.dnsrch). If a search list is specified, the default local
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domain is not used on queries. </p>
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</div>
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<div class="section"><h4 class="sectiontitle">RES_OPTIONS </h4><p>The RES_OPTIONS environment
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variable allows certain internal resolver variables to be modified. The environment
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variable can be set to one or more of the following space-separated options:</p>
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<ul><li><strong>NDOTS: n</strong> Sets a threshold for the number of dots
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that must appear in a name given to <span class="apiname">res_query()</span> before
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an initial absolute query is made. The default for n is 1, meaning that if
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there are any dots in a name, the name is tried first as an absolute name
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before any search list elements are appended to it. </li>
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<li><strong>TIMEOUT: n</strong> Sets the amount of time (in seconds)
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that the resolver waits for a response from a remote name server before giving
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up and trying the query again.</li>
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<li><strong>ATTEMPTS: n</strong> Sets the number of queries that the
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resolver sends to a given nameserver before giving up and trying the next
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listed name server. </li>
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<li><strong>ROTATE:</strong> Sets RES_ROTATE in _res.options, which rotates the selection
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of nameservers from among those listed. This has the effect of spreading the
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query load among all listed servers, rather than having all clients try the
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first listed server first every time.</li>
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<li><strong>NO-CHECK-NAMES:</strong> Sets RES_NOCHECKNAME in _res.options, which disables
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the modern BIND checking of incoming host names and mail names for invalid
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characters such as underscore (_), non-ASCII, or control characters. </li>
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</ul>
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</div>
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<div class="section"><h4 class="sectiontitle">QIBM_BIND_RESOLVER_FLAGS</h4><p>Set this environment variable
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to a space separated list of resolver option flags. This overrides the RES_DEFAULT
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options (struct state.options) and system configured values (Change TCP/IP
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Domain - CHGTCPDMN). The state options structure is initialized normally,
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using RES_DEFAULT, OPTIONS environment values and CHGTCPDMN configured values.
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Then this environment variable is used to override those defaults. The flags
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named in this environment variable might be prepended with a '+', '-' or 'NOT_'
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to set ('+') or reset ('-','NOT_') the value. </p>
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<p>For example, to turn
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on RES_NOCHECKNAME and turn off RES_ROTATE, use the following command from
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a character-based interface: </p>
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<pre> ADDENVVAR ENVVAR(QIBM_BIND_RESOLVER_FLAGS) VALUE('RES_NOCHECKNAME NOT_RES_ROTATE')</pre>
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<p>or</p>
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<pre> ADDENVVAR ENVVAR(QIBM_BIND_RESOLVER_FLAGS) VALUE('+RES_NOCHECKNAME -RES_ROTATE')</pre>
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</div>
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<div class="section"><h4 class="sectiontitle">QIBM_BIND_RESOLVER_SORTLIST</h4><p>Set this environment
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variable to a space-separated list of up to ten IP addresses/mask pairs in
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dotted decimal format (9.5.9.0/255.255.255.0) to create a sort list (struct
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state.sort_list).</p>
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</div>
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</div>
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<div>
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<div class="familylinks">
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<div class="parentlink"><strong>Parent topic:</strong> <a href="dns.htm" title="iSeries provides applications with access to the Domain Name System (DNS) through the resolver functions.">Domain Name System support</a></div>
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</div>
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<div class="relinfo"><strong>Related information</strong><br />
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<div><a href="../apis/resini.htm">res_init()</a></div>
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<div><a href="../apis/resninit.htm">res_ninit()</a></div>
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<div><a href="../apis/resqry.htm">res_query()</a></div>
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</div>
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</div>
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